Synchronous electric motor



May 25, 1948. c. swxFT 2,442,316

SYNCHRONOUS ELECTRIC MOTOR Filed April 9, 1947 Treas Suf/Fr Patented May 25, 1948 UNITED STATES PATENT OFFICE 12 Claims. 1

My invention relates to synchronous motors of the inductor type and its object is to provide an emcient, low-speed, self-starting, quiet operating motor particularly adapted to be built in fractional horsepower sizes, for the operation of timing devices such, for example, as cloc is, phonographs and the like.

A further object of my invention is to provide an improved synchronous motor of the inductor type having features of construction, combination and arrangement wherein simple and easily produced parts may be used to the end that the cost of construction thereof is minimized.

Further it is an object of my invention to provide an improved synchronous motor of the inductor type wherein cost is reduced by the use of parts having identical construction.

It is yet another object of my invention to provide an improved rotor element for inductor type synchronous motors which is adapted to be produced by low cost stamping operations.

The features of my invention which are believed to be novel and patentable will be pointed out inthe claims appended hereto. For a better understanding of my invention reference is made to the following description, taken in connection with the accompanying drawings.

On the drawings:

Figure 1 is a top view of a completed motor constructed in accordance with my invention;

Figure 2 is a cross-sectional view taken through the axis II-II of Figure 1;

Figure 3 is a view showing the various oomponent elements of the motor of Figure 1; and

Figure 4 is a cross-sectional view like Figure 2 but showing a modied form of the present invention employing a plastic casing structure.

As shown on the drawings:

The motor of my invention includes an upper stator element Il] which is stamped of steel or other high permeability material. This element engages lower stator element I2 which is constructed of similar material and is likewise stamped. Lower stator element I2 includes an inwardly extending portion l4 which is provided with an opening to receive permanent magnet i6, the magnet IE being disposed so that its magnetic field extends in direction perpendicular to the plane of inwardly extending portion I4 ofvlower stator element I2. Solenoid 8 is wound about magnet I5 so as to produce a magnetic eldin direction corresponding to the direction of a magnetic eld of magnet IE. Solenoid I8 isconnected to a source of alternating electromotive force shown schematically: at I9.

Upper stator element IB is provided with inwardly extending portion 2Q which has downwardly extending portion 22 to receive the upper stator 24. The inwardly extending portion of lower stator element I2 is provided with an upwardly extending portion 2% adapted to receive lower stator 28. in addition, magnet I6 contains bearing Sn which shaft 32 rides. Upon this shaft are mounted rotor 34 and flywheel 35. Upper stator 24, lower stator 28 and rotor 34 are made of relatively high permeability material, such as steel.

The construction oi upper stator 24, lower stator 23, and rotor 34 will be evident from examination of the cross-section view of Figure 2 and the plan views of Figure 3. In the latter ligure, the upper stator element IB is lifted onc the lower stator element I2 and faces upwardly and the rotor 34 removed from the stator and likewise faces upwardly. 1t will be apparent that each of these elements is of cylindrical shape having an inwardly extending flange. In the oase of rotor 34, this flange extends to the point where it is engaged by support 38 which is attached to shaft 32, thereby supporting rotor 34 relative to shaft 32. In the case of upper stator 24 and lower stator 28 the inwardly extending portions are of relatively narrow annular shape and merely engage the correspondingly recessed portions 22 and 2S of upper stator element Sil and lower stator element I2 respectively.

The shape of lower stator 28, upper stator 24, and rotor 34 is such that as a periphery of these elements is traversed, periodic variations in radius are encountered. That is, these elements have the wavy configurations shown in the plan view of Figure 3. From the view of Figure 2, it will be' evident that rotor 34 overlaps upper stator 24 in the direction of shaft 32 to substantially the same extent that it overlaps lower stator 23.

Mounting flanges 4i! are provided for lower stator element I2 to permit convenient mounting of the motor on the support provided for this purpose.

I 6. The second ilux path is from the upper portion of magnet -I through rotor 34 and through the upper stator 24, the upper stator element Il), and lower stator element I2 to the lower portion of magnet I'S. The lpath for flux associated with alternating current iiow in solenoid I8 is from lower stator 28 to rotor 34 and therefrom to upper stator 2:4. From upper stator 24 the flux passes through upper sta-tor element lili and lower stator element I 2 to lower stator 28 to complete the circuit. It will be observed that the flux associated with a unidirectional field dueto magnet I5 is always in the same direction between rotor 34 and stators 24 and 28 whereas the alternating liux passes from stator 28 to rotor 34 and from stator 24 to rotor 34 in opposite directions.

In operation, the iiux associated with passage of alternating current through coil I8 alternately supports and opposes the flux from magnet I6 between rotor ,5,4 and stator 28 and between stator '24 and rotor 34. YThus there is first set up addi- Ational flux between rotor 34 and stator 24 so as -tocause thev points of maximum radius of roto-r 34 to line upwith points of minimum radius of stator .24.. On theA next half cycle of alternating current flow in ,coil'IlL the iiux between rotor 34 and stator 23 V,is increased, thereby causing the pointsof maximumY radius of rotor 34 to line up with pointsof Vminirvmun radius of stator 28. However, stators 24 and 28 are rotated relative to each other Yby a small amount so that in going from the position `wherein points of maximum radiusof rotor 3.4lineup with the points of minimum radius of stator ,24 to the position where the. lpoints of. maximum radius of rotor 34 line up withgthe pointsof minimumv radius of stator 28, the rotor 34 rotates. Dueto the symmetrical construction ofA stator elements 24 and 28 and rotor 34,V the next half cycle of alternating cur-l rent requires further motion of rotor 34 in the same direction,V thus causing continuous rotor vmotion.

It willbe apparent from the above description thatthe torque applied to rotor 34 by reason of the operation or the motor is pulsating. The eiect of these variationson the operation of the :motor is reduced by :providing iiywheel 36 which has a relatively great inertia and maintains substantially constant velocity motion despite the torque variation.

Figure 4 shows a modiedfforin of the present invention wherein a plastic'Y casing comprising members -Ia and I2a is substituted for the upper andlower stator elements IIJ and I2 of Figure 2. As .will be evident from Figure 4, lower stator 28 is mounted.l within pipe section 42 which is of iron or other magnetic material and is retained in thetlower plastic casing portion I2a. A ring or washer 444 of iron or other magnetic material frictionally engages the inner side of pipe 42 and the lower end of the cuter periphery of magnet I6, thus holding these elements in lixed position relative to each other. The upper stator element 24 is sustained by upper pipe section 46 which is supported by the plastic casing section Illa.

It will be evident from comparison of Figures 2 and 4 that `the alternate embodiment of my invention shown in Figure 4 differs from that of Figure 2 primarily in that the plastic casing comprising elements Illa and I2a is substituted for the high` permeability upper and lower stator elements Ill rand I2'. ItV will be evident to those skilled. in the art that this construction is considerably less expensive than the structure shown 4 in Figure 2, since the plastic part may be cheaply molded.

Operation of the embodiment of the present invention vshown in Figure 4 is like that of the embodiment of Figure 2 except that the plastic casing including elements IUa and I2a has unity magnetic permeability and hence does not provide a low reluctance flux path about coil I8. However, I have found that this structure works quite satisfactorily and the shaft' 32rotates in the same manner as in the case of the structure of Figure 2 when alternating voltage is applied Yto coil I 8. This is apparently due to the fact that suiiicient flux exists to produce the necessary torque on the rotor in the low torque applications to which the motor has been applied.

A particularly important feature of my invention resides in the construction of rotor element 34 and stator elements 24 and 28 so that they may be manufactured by stamping operations. This permits relatively inexpensive construction of my motor despite the complicated casing that might seem to be required. It is further possible to use stampings for lower stator I2 and upper stator Il so as to avoid entirely the need for machined parts and the consequent expensive construction.

In accordance with the provisions of the patent statutes ,I have described the principles of operation of myinvention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood Vthat the apparatus shownV is only illustrative and that the invention mat7 be carried out by other means. In particular, the rotor construction. of my invention may be utilized on reluctance type motors of other constructions than that specically shown herein, and' many of the advantages of my .invention thereby secured.

What I claim as new and desire to secure by Letters Patent in the United States is: Y

1. An electric motor comprising inV combination a solenoid, a magnet Vdisposedwithin said solenoid and having a magnetic field coaxial with the magnetic eld of said solenoid, a. casing of relatively high permeability material forming a magnetic circuit about said solenoid and passing between saidsolenoid and said ma-gnet, said circuit having an air gap .in substantial alignment with one end ofv said magnet, said casing being Iof cylindrical shape in the. regions immediately above and below said air gap and having periodic variations in radius as the periphery thereof is traversed, and a rotor element of relatively high permeability disposed betweenv said magnet and said .casing in the region of said gap, said rotor being of cylindrical shape having pericdicvariations inradius as its periphery is traversed, the variations in radius of said regions of said casing being angularly displaced relative to each other so that application of alternating voltage to said solenoid produces torque .on said rotor. y Y

2. An electric motor comprising in combination, a solenoid, a magnet disposed within said solenoid and having a magnetic iield coaxial with the magnetic eld of said solenoid, a casing of relatively high permeability material form-V ing a magnetic circuit aboutA said solenoid and passing between said solenoid and said magnet, said circuit having "an air gap substantially valigned with one end of said magnet, said casing of said regions having periodic variations in radius as the periphery thereof is traversed, a rotor element of relatively high permeability material disposed between said magnets and said casing in the region of said gap, said rotor being of cylindrical shape having periodic variations in radius as its periphery is traversed, the variations in radius of said regions of said casing being angularly displaced relative toeach other so that application yof alternating voltage to said solenoid causes rotation of said rotor, and a ilywheel on said rotor to limit variations in the angular velocity thereof.

3. An electric motor comprising in combination a rotor and a pair of stators mounted coaxially therewith, said rotor comprising a cylindrically shaped member having recurrent variations in radius as its periphery is traversed and said stators having recurrent variations in radius as their peripheries are traversed, said stators and said rotor being of relatively high permeability material, one of said stators being telescoped with the upper portion of said rotor and the other of said stators being telescoped with the lower portion oi said rotor, and means operable alternately to produce greater magnetic ux between one ci said stators and said rotor and between the other of said stators and said rotor, the recurrent variations in radius of said stators being angularly displaced relative to each other so as to cause rotation of said rotor.

4. An electric motor comprising in combination a rotor and a pair of stators mounted coaxially therewith, said rotor comprising a stamping having a flange and an axially extending cylindrical portion with recurrent variations in radius as its periphery is traversed and said stators having recurrent variations in radius as their peripheries are traversed, said stators and said rotor being of relatively high permeability material, one of said stators being telescoped with the upper portion of said rotor and the other of said stators being telescoped with the lower portion of said rotor, and means operable alternately to produce greater magnetic flux between said one stator and said rotor and between said other stator and said rotor, the recurrent variations in radius of said stators being angularly displaced relative to each other so as to cause rotation of said rotor.

5. An electric motor comprising in combination a rotor and a pair of stators mounted coaxially therewith, said rotor comprising a cylindrically shaped member having recurrent variations in radius as its periphery is traversed and said stators having recurrent variations in radius as their peripheries are traversed, one of said stators being telescoped with the upper portion of said rotor and the other of said stators telescoped with the lower portion of said rotor, said stator and said rotors being of relatively high permeability material, and means operable alternately to produce greater magnetic flux between one of said stators and said rotor than between the other of said stators and said rotor, the recurrent variations in radius of said stators being angularly displaced relative to each other so as to cause rotation of said rotor, said means including means to produce a unidirectional magnetic eld between said rotor and said stators and means to produce an aternating magnetic field between said stators.

6. An electric motor comprising in combination a rotor and a pair of stators mounted coaxially therewith, said rotor comprising a stamping having a ilange and an axially extending cylindrical portion with recurrent variations in radius as its periphery is traversed and said stators having recurrent variations in radius as their peripheries are traversed, one of said stators being telescoped with the upper portion of said rotor and the other of said stators being telescoped with the lower portion of said rotor, said stators and said rotors being of relatively high permeability material, and means operable alternately to produce greater magnetic flux between .one of said stators and said rotor than between the other of said stators and said rotor, the recurrent variations in radius of said stators being angularly displaced relative to each other so as to cause rotation of said rotor, said means including means to produce a unidirectional magnetic eld between said rotor and said stators and means to produce an alternating magnetic eld between said stators.

7. In an electric motor, a cup-shaped rotor oi material of relatively high permeability having a skirt portion with periodic variations in radius as its periphery is traversed, a pair of oppositely disposed cup-shaped stator elements of material oi' relatively high permeability each having an axially extending skirt portion having periodic variations in radius as its periphery is traversed, means mounting said stator elements coaxially with said rotor element and with their periodic variations in radius angularly displaced relative to each other, a magnet core to engage said stator elements to provide a flux path therebetween, a permanent magnet mounted coaxially with said rotor and having one end adjacent the ends of said stator elements and the other end magnetically connected to said core, and a solenoid disposed to produce ilux in said core so that application of alternating electromotive force thereto causes rotation of said rotor.

8. An electric motor comprising a pair of oppositely disposed cup-like frame members of relatively high permeability material, a pairAof oppositely disposed cup-like stators, each having a skirt portion with periodic variations in radius as its periphery is traversed, said frame members having recesses snugly to receive said stators so that they are mounted in coaxial relation with an intervening air gap, said stators being of relatively high permeability material, a rotor element of relatively high permeability material mounted coaxially with said stators, said rotor being of cylindrical shape with periodic variations in radius as its periphery is traversed and being mounted in axial alignment with the gap between said stators, a permanent magnet mounted coaxially with said rotor with one end mounted in one of said frame members and the other end axially aligned with the gap between said stators, and a solenoid mounted within said frame members but outside said stators, said stators being disposed so that their periodic variations in radius are angularly displaced so that application of alternating electromotive force to said solenoid rotates said rotor.

9. An electric motor comprising in combination a rotor and a pair of stators mounted coaxially therewith., said rotor comprising a cylindrically shaped member having a smoothly varyinnT radius from a minimum and a maximum value as its periphery is traversed and said stators having smoothly varying radii from a minimum to a maximum value as their peripheries are traversed, said stators and said rotor being of relatively high permeability material, one of said stators being telescoped with the lower portion of said rot'or,V andthe `other of said stators being telescoped with the upper portion of said rotor, and

operable alternately to produce greater magnetic ux between one of said stators and said rotor than between the other of said stators Aand "said rotor, the variations in radius of said stators being angularly displaced relative to each other so as to cause rotation of said rotor.

10. An electric motor comprising in combination a solenoid, a magnet disposed within said ysolenoid and having a magnetic field coaxial with the magnetic ield of said solenoid', elements defining a magnetic flux path within said solenoid, said path having anair gap in substantial alignment with one of said magnet, said `elements being of cylindrical shape in the sections immediately above and below said air gap and having periodic variations in radius as the peripheries thereof are traversed, and a rotor of relatively high per- Y meability material disposed in telescoping relation` with Said elements, said rotor being of cylindrical shape having periodic variations in radius as its periphery is traversed, the variations in radius of said elements being angularly displaced relative to each other so ythat the application of alternating voltage to said solenoid produces torque on said rotor.

1'1. An electric motor comprising in combination a solenoid, a magnet disposed within said solenoid and having a magnetic ield coaxial with the magnetic field of said solenoid, elements dening a magnetic iiux path passing between said solenoid and said magnet, said elements having an air gap in substantial alignment with one end of said magnet, said elements being of cylindrical shape in the regions immediately above and below said air gap and having periodic variations in radius as the peripheries thereof are traversed, and a rotor element of relatively high perme- 8 ability lmaterial disposed lbetween said magnet and Asaid casing in the region of said gap, 'sa`1d rotor being of lcylindrical shape having periddi'c variations in radius as its periphery 'is traversed, the variations in radius of said region 'df said casing being a'ngularl'y displaced relative to eachother so that application ifalternating volt- Y age to said solenoid produces torque o n said rotor, and a casing of plastic or the like dis-posed 'to support lsaid elements and to form an enclosure for said solenoid. i

12. An electric motor comprising Vtwo members of relatively high permeability material having aligned cylindrical cavities with periodic variations in radius as their-peripheries are traversed, a rotor of relatively high permeability material having a cylindrical portion of smaller diameter than the diameter of said cavities and having periodic variations in radius as its periphery is traversed, said rotor being positioned in telescoping relationship with said members, means dening a magnetic circuit between said members, Y

a solenoid linking said circuit, and means to produce a uni-directional magnetic eld between said rotor and said members, the variations'in radius of the cavities of said members being angularly displaced relative to each other to cause torque on said rotor when said solenoid is energized with alternating electromotive force.

CYR-US SWIFT.

REFERENCES crrizn The following references are of record in the le of this patent:

NITED STATES PATENTS Name bate Y 

